1. Field of the Invention
The present invention relates to an improvement of a radius end mill used for a contour line engraving operation, etc. for metal molds, etc., and particularly to an improvement of a radius end mill used for high-feed cutting.
2. Description of the Related Art
A ball-nose end mill has been generally used to subject metal molds, etc. to a contour line engraving operation. Recently, high-efficiency cutting has been strongly required, and a radius end mill has been more frequently used in place of the ball-nose end mill.
As compared with the ball-nose end mill, the cutting edges of the radius end mill are brought into contact with a workpiece at a shorter length. In addition, it is impossible to achieve a high cutting (milling) speed for the ball-nose end mill because the tip portion of the ball-nose end mill is located on the tool rotation axis of the ball-nose end mill. On the other hand, it is possible to achieve a sufficiently high cutting (milling) speed for the radius end mill, so that the radius end mill has a low cutting force, cuts cleanly and is suitable for high-efficiency cutting.
In addition, with respect to the radius end mill, various improvements have been made in accordance with the intended use thereof. For example, JP-A-7-246508 discloses an improvement to reinforce a corner R edge, and JP-A-11-216609 discloses an improvements to enhance cutting performance (machinability).
Furthermore, a long tool-overhang length working such as a corner working, a deep-cutting working or the like has been known as a working of metal molds, etc. Chattering vibration is liable to occur during cutting (milling) in such working processes, and thus these working processes adopt a method in which a table feed speed of an end mill feed is reduced because this feed-reducing method is easily processed on the basis of NC programs. According to the feed-reducing method, not only the working efficiency is reduced, but also an effect of suppressing chattering vibration is lowered and thus a feed per tooth is proportionally reduced. Therefore, the contact frequency of a cutting edge with a workpiece is increased and wear is promoted.
In addition, there is known a method in which a cutting (milling) speed is reduced with keeping the chattering vibration suppressing effect high. However, only this method reduces the feed proportionally, and at any rate the working efficiency is lowered. Recently, high-feed cutting in which the cutting (milling) speed is reduced, however, the table feed speed is increased, that is, the feed per tooth is extremely increased has been used as high-efficiency cutting means.
However, the radius end mill has had such a problem that when the feed per tooth is extremely increased, the cutting load is concentrated to corner R edges and the mechanical strength of the corner R edges is unendurable to the cutting load, so that the corner R edges are chipped or fractured and come to the ends of their lives. Particularly, when the high-feed cutting is carried out in a cutting working needing a large cutting amount such as a rough working or the like, the cutting force is large and the chipping further easily occurs, so that the cutting condition must be loosened. This means that the present cutting condition has not yet reached the high-efficiency cutting.